Protective device

Abstract

A protection device including: (i) a protection component having a first thermal fuse and a resistive body, the resistive body being supplied with a current in an abnormal state to generate heat, the heat activating the first thermal fuse to cut off the current; (ii) a PTC component; and (iii) a second thermal fuse, the second thermal fuse being electrically connected in series to the PTC component, the first thermal fuse of the protection component being electrically connected in parallel to the PTC component and to the second thermal fuse, and the protection component being activated in the abnormal state so that the PTC component trips to generate heat, the heat blowing the second thermal fuse.

The invention claimed is: 
     
       1. A protection device comprising:
 (i) a protection component comprising a first thermal fuse and a resistive body wherein in an abnormal state the resistive body is supplied with a current to generate heat, and by the heat the first thermal fuse activates to cut off the current; 
 (ii) a PTC component; and 
 (iii) a second thermal fuse, 
 wherein the second thermal fuse is electrically connected to the PTC component in series, 
 the first thermal fuse of the protection component is electrically connected to the PTC component and to the second thermal fuse in parallel, and 
 by activating the protection component in the abnormal state, the PTC component trips to generate heat, and the heat fuses the second thermal fuse; 
 wherein an activating time of the PTC component is longer than an insulation time of a fuse element of the first thermal fuse. 
 
     
     
       2. The protection device according to  claim 1 , wherein the protection component is a fusing resistor. 
     
     
       3. The protection device according to  claim 2 , wherein
 the fusing resistor has a pair of lead fixed electrodes, a guide shaft is juxtaposed to the lead fixed electrodes, wherein 
 a movable electrode is disposed such that it bridges the lead fixed electrodes while being inserted into the guide shaft, 
 a tip of each of the lead fixed electrodes and the movable electrode are joined with a low-melting-point alloy, and the guide shaft and the movable electrode is joined with a low-melting-point alloy, 
 a compression spring is provided which applies a force to the movable electrode in a direction away from the lead fixed electrodes, and 
 when the low-melting-point alloy is melted, the compression spring presses the movable electrode so that the movable electrode separates from the lead fixed electrodes. 
 
     
     
       4. The protection device according to  claim 3 , wherein
 in the fusing resistor, one lead conductor of a resistor having lead conductors fitted to both ends of the resistive body is used as the guide shaft, 
 a coil spring is used as the compression spring, 
 the coil spring is inserted in the one lead conductor between the resistive body and the movable electrode, and 
 a circuit applying a current to a resistor for generating a heat is connected between the one lead conductor of the resistor and either one of the two lead fixed electrodes. 
 
     
     
       5. The protection device according to  claim 1 , wherein the PTC component is a polymer PTC component. 
     
     
       6. The protection device according to  claim 1 , wherein a resistance value of the PTC component at a use temperature is equal to or less than a rated voltage of the protection component/abnormal current. 
     
     
       7. The protection device according to  claim 5 , wherein a resistance value of the PTC component at a temperature lower 10° C. than a softening point of a polymer material of the polymer PTC component is equal to or less than a rated voltage of the protection component/abnormal current. 
     
     
       8. The protection device according to  claim 1 , wherein an activating time of the PTC component is 3 milliseconds or more. 
     
     
       9. The protection device according to  claim 1 , further comprising one or more PTC components electrically connected to the PTC component in parallel and electrically connected to the second thermal fuse in series. 
     
     
       10. The protection device according to  claim 1 , wherein an activation temperature of the second thermal fuse is lower than a trip temperature of the PTC component. 
     
     
       11. The protection device according to  claim 1 , wherein a fusing time of the second thermal fuse at an abnormal current is longer than a tripping time of the PTC component. 
     
     
       12. The protection device according to  claim 1 , wherein the second thermal fuse has a withstand voltage equal to or more than an abnormal voltage at a leak current when the PTC component is in its tripping state.